1. Field of the Invention
The present invention relates to a roll coater control method and a roll coater for coating a required coating solution such as a photoresist solution in a uniform thickness on the surface of a substrate such as that of glass, ceramic or silicon.
2. Description of the Prior Art
FIG. 10 shows a conventional roll coater well known as an apparatus for coating a photoresist solution on the surface of a substrate of glass, ceramic or silicon. This roll coater retains a coating roll 1 to be rotatable about a horizontal axis through a bearing 1a while retaining the bearing 1a vertically movable through cylinders 6 so that the coating roll 1 can be in contact with/separated from a back-up roll 3. A pair of such cylinders 6 are provided in correspondence to both ends of the coating roll 1, to independently drive the ends of the coating roll 1 to be in contact with/separated from the back-up roll 3. A doctor roll 2 is retained to be rotatable about a horizontal axis through a bearing 2a, which is reciprocably retained by cylinders 7 so that the doctor roll 2 can be in contact with/separated from the coating roll 1. A pair of such cylinders 7 are provided in correspondence to both ends of the doctor roll 2, to independently drive the said ends of the doctor roll 2 to be in contact with/separated from the coating roll 1.
A coating operation is performed by rotating the respective rolls 1, 2 and 3 in the directions indicated by arrows while locating the same in positions as shown in FIG. 10. The a coating solution 60 is supplied between the rolls 1 and 2 from a nozzle 5, and a substrate 10 is fed between the rolls 1 and 3 by a carrier roll 4. Thus, the coating solution 60 supplied from the nozzle 5 is coated on the surface of the substrate 10 through the coating roll 1.
FIG. 11 is a schematic view showing another example of a conventional roll coater. This roll coater is different from that shown in FIG. 10 merely in that a doctor bar 8 as shown in FIG. 11 is employed in place of the doctor roll 2 as shown in FIG. 10.
In each of the conventional roll coaters, the pressure applied to both end shafts of the coating roll 1 can be adjusted through the cylinders 6 and a vertical movement adjusting screw (not shown) in order to uniformly adjust the film thickness of the coating solution coated on the surface of the substrate 10. However, it is difficult to finely adjust the amount of vertical movement of the coating roll 1 by the cylinders 6. Thus, when the board thickness of the substrate 10 is varied, the coating solution cannot be adjusted to be in the prescribed thickness in response to the varied board thickness of the substrate 10.
In each of the said roll coaters, the volume of the coating solution coated on the surface of the coating roll 1, i.e., the film thickness of the coating solution, can be adjusted by controlling the amount of pushing of the doctor roll 2 or the doctor bar 8 against the coating roll 1, i.e., the amount of pressure applied from the cylinders 7 to the doctor roll 2 or the doctor bar 8. Also in this case, however, it is difficult to finely adjust the amount of reciprocation of the doctor roll 2 or the doctor bar 8 by the cylinders 7, whereby the film thickness of the coating solution applied to the surface of the coating roll 1 cannot be adjusted. In this case, it is possible to finely adjust the pressure applied to the doctor roll 2 or the doctor bar 8 by the cylinders 7 manually through a distance adjusting bolt (not shown). In that case, however it is impossible to automatically adjust the film thickness.
In order to automatically adjust the film thickness, the following structure may be employed in place of the cylinders 6 and 7 in each of the aforementioned roll coaters. Namely, pulse motors and screw rods rotatably driven by the pulse motors may be employed so that the screw rods are respectively engaged with the bearings 1a on both ends of the coating roll 1 and the bearings 2a on both ends of the doctor roll 2. Then the pulse motors are adapted to adjust the vertical movement of the coating roll 1 and the reciprocation of the doctor roll 2. However, such structure causes the following new problems. In general, errors in working accuracy on the surfaces of the rolls 1 and 2 may cause one end of such a roll to be different in diameter from the other end. Further, the amount of movement at one end of the roll may not correspond to that at the other end due to tolerance between the screw rods and the bearings 1a and 2a or to screw working errors of the screw rods. Thus, when the rolls 1 and 2 are driven to be in contact with/separated from each other, outer peripheral surfaces of the opposing rolls 1 and 3 or 1 and 2 may not be parallel with each other, whereby the coating film formed on the surface of the substrate 10 is nonuniform in thickness.